Research in brain function may be roughly divided into various levels (from microscopic to macroscopic), e.g. gene expressions, protein biochemical reactions, neuronal functions, brain neural network organizations and animal behavior. Molecular biology, flourished since the 1960s, allows genetic manipulation to reflect biological functions at different scales. In such ways, researchers can now make use of technology to identify Drosophila memory genes of olfaction and memory and alter these genes to influence its behavior. Although scientists have a clear understanding of macro-scale biology such as animal behavior and micro-scale biology such as gene expression and perspectives of biology, micro-meso-scale biological research remains under-studied owing to technical limitations which including the difficulty to acquire the 3D structure of nerve cells and cerebral neural networks. Now, the integration of biofluorescent labeling and optical section scanning in confocal microscopy gives rise to the possibility of high-resolution digital images of the brain and its neural network.
Biologists often can not obtain images (information) of an organism's internal structure without damaging the organism itself. Furthermore, when acquiring biological images, physical limitations of laboratory equipment could only generate a serial of two-dimensional (2D) images instead of three dimensional images; as a result, the spatial information between organs is not immediately made available. While an invention in 2002, U.S. Pat. No. 6,472,216 presents a sample preparation solution which enables scientists to acquire images from a transparent whole mount samples.
Owing to the technological advances in the twentieth century, it is generally accepted that a completely modular brain model can depict its functional reality. Therefore, the interpretation of brain function can be analytically and anatomically described based on the interactions among different brain regions or even neurons. Accordingly, 3D image reconstruction technology can be exploited to build models of major compartments of the brain, and at the same time, merge the anatomy of neuropils or neurons with the function of neural networks in the brain.
Neuropil is a region between neuronal cell bodies in the gray matter of the brain and spinal cord (i.e. the central nervous system). It consists of a dense tangle of axon terminals, dendrites and glial cell processes. It is where synaptic connections are formed between branches of axons and dendrites.
Although the information processing and transmission of the human brain fascinates scientists the most, the fact that the human brain has 100 billion neurons, plus human's relatively longer life span and genes that cannot be manipulated at will, has limited neuroscience research on human brain structures at the cellular level. Scientists thus turn their investigation to other organisms, e.g. mice, zebrafish and Drosophila. For instance, the Drosophila brain only has about 135,000 neurons, but can still exhibit complex memory and learning behaviors; consequently, it has become one of the most popular and important research targets in neuroscience. In addition, Drosophila genes have been entirely sequenced, and its short life cycle (approximately 60 days) further makes it a valuable research target. The knowledge obtained from studies of neural networks in Drosophila may be extended to systems with much more complexities such as human brains (Armstrong, JD and Van Hemert JI, 2009 Towards a virtual fly brain Phil. Trans. R. Soc. A 367, 2387-2397).